Interannual Variability of Tropical Atlantic-to-Pacific Moisture Transport Linked to ENSO, Atlantic Niño, and Freshwater Budget in the Northwestern Tropical Atlantic

Abstract

Moisture transport from the Atlantic to Pacific is important for basin-scale freshwater budget and the formation of meridional ocean circulation. Although the climatological tropical Atlantic-to-Pacific moisture transport (TAPMORT) has been well investigated, few studies have focused on its variability. Here we investigate the interannual variability of TAPMORT based on the atmospheric reanalysis data sets. The TAPMORT interannual variability is dominated by the variations of trans-basin winds across Central America, and peaks in late boreal summer and late boreal winter. 1) In late summer, a developing El Niño and a mature Atlantic Niña set up an interbasin sea-surface temperature (SST) gradient that strengthens the low-level jet across Central America and therefore TAPMORT (with weakened TAPMORT for opposite signed events). This process typically occurs from July to September, with a peak in August. 2) In late winter, the strengthened southern North American center of the Pacific-North American-like pattern intensifies the TAPMORT variations. Although atmospheric interannual variability dominates these variations, extreme El Niño events are also important for the teleconnections. This process shows a single peak in February, in contrast to the persistent peak in late summer. We further demonstrate that the persistent TAPMORT variability in late summer dominates the moisture divergence over the northwestern tropical Atlantic and modulates freshwater flux there. Thus, our study improves the understanding of how TAPMORT interannual variability and the related interbasin SST gradient regulate the northwestern tropical Atlantic freshwater budget and the related salinity variability.

The Role of Atmospheric Transport for El Niño‐Southern Oscillation Teleconnections

“…Ropelewski and Halpert (1987) found dry conditions from July to October, but no clear signal for DJF. For boreal late summer reduced precipitation was found during EN by Yang et al (2021). Based on this the tagged air seems to act as a negative feedback.…”

“…For boreal late summer reduced precipitation was found during EN by Yang et al. (2021). Based on this the tagged air seems to act as a negative feedback.…”

Optimal Growth of IPV Lags AMV Modulations by up to a Decade

“…The result is similar when using CMIP6 models. Finally, we smooth the internal annual‐mean data with a 5‐year running mean method to obtain the decadal component of variability (Yang et al., 2021). The 5‐year running mean internal SST variations in the tropical Pacific are shown (Figures 1a and 1b).…”

A Lagrangian Perspective on the Atlantic and Pacific Precipitation‐Evaporation Asymmetry

“…The 𝐴𝐴 𝐴𝐴 𝐴𝐴𝐴𝐴𝐴𝐴 𝑛𝑛 profile is characterized by three distinct maxima in Central America associated with gap winds through the orography with the peak at 11°N above Lake Nicaragua in the Papagayo jet (Clarke, 1988). The maxima occur between 850 and 900 hPa, the approximate pressure levels of these gap winds, similar to cross-sections of velocity, water vapor mixing ratio and moisture transport anomalies (Xu et al, 2005;Yang et al, 2021). This demonstrates the smaller role of moisture transport above Panama compared to its neighbors further north in this region despite some studies (Leduc et al, 2007;Lohmann, 2003;Sinha et al, 2012;Zaucker & Broecker, 1992) previously assuming that this moisture flux was the key reason for the contrasting Pacific and Atlantic 𝐴𝐴 𝑃𝑃 − 𝐸𝐸 values.…”